In a commercial alkylation plant, for example, acid is used as catalyst to produce gasoline by the alkylation of C.sub.3 -C.sub.5 olefins and alkanes. The catalytic acids include sulfuric acid, hydrogen fluoride, and solid acid. Only sulfuric acid and hydrogen fluoride are commercialized nowadays. Because hydrogen fluoride is very toxic, hydrogen fluoride is gradually being phased out in the alkylation process. The most popular catalyst used to manufacture gasoline from the alkylation of C.sub.3 -C.sub.5 olefins and alkanes is concentrated sulfuric acid. The ratio of sulfuric acid to organic compounds in the alkylation reaction vessel is 0.1.about.0.3, so the amount of concentrated sulfuric acid required in the alkylation process is very large. In general, producing one ton of gasoline makes 0.1 ton spent sulfuric acid. If ten thousands barrels of gasoline are produced a day, one hundred tons of spent sulfuric acid are produced. Such a large amount of spent sulfuric acid can not be cast away or stored, it must be treated in advance. Based on the above description, the key point of alkylation is the treatment or regeneration of the spent sulfuric acid in refinery site and in situ reuse in the alkylation unit, i.e. an integrated process of the combination of alkylation and regeneration.
A lot of products of alkylation processes using sulfuric acid as catalyst were raised by L. F. Albright and A. R. Goldsby, "Industrial and Laboratory alkylations" in ACS symposium series 55, p.91, Washington, D.C., 1977, as shown in Table 1.
TABLE 1 ______________________________________ Composition of alkylates obtained over H.sub.2 SO.sub.4 hydrocarbons composition ratio ______________________________________ isopentane -- n-pentane -- C.sub.5 8.9 2,3-dimethylbutane 4.7 2-methylpentane 1.1 3-methylpentane 0.4 C.sub.6 6.2 2,2,3-trimethylbutane 0.2 2,2-dimethylpentane 0.2 2,4-dimethylpentane total 2-methylhexane 3.4 3-methylhexane 0.3 2,3-dimethylpentane 2.3 C.sub.7 6.4 2,2,4-trimethylpentane 24.3 2,2,3-trimethylpentane 1.2 2,3,3-trimethylpentane 12.3 2,3,4-trimethylpentane 13.0 2,2-dimethylpentane 0.2 2,3-dimethylpentane total 2,4-dimethylpentane 3.0 2,5-dimethylpentane 6.6 3,4-dimethylpentane 0.4 C.sub.8 61.0 c.sub.9 and higher 17.5 ______________________________________
The organic products may reside in the sulfuric acid to form said organic impurities, and the water contained in the raw material of alkylation or generated during alkylation may accumulate in the sulfuric acid, so the spent sulfuric acid must be regenerated to remove both the organic impurities and the water.
In order to treat the spent sulfuric acid in a commercial alkylation plant, a sulfuric acid plant is usually set up. The procedure of the treatment of sulfuric acid is described as following. First of all, spent sulfuric acid, air, and fuel are sent into the combustion chamber to burn out the organic impurities and sulfuric acid into SO.sub.2, SO.sub.3, CO.sub.2, H.sub.2 O and ashes, etc. After drying the gases from the combustion chamber, the dried gases are purified to remove impurities and ashes in order to get pure SO.sub.2. The SO.sub.2 gas reacts with air or oxygen to convert to SO.sub.3 at high temperature using V.sub.2 O.sub.5, etc. as catalyst. The SO.sub.3 gas is absorbed twice by water to get concentrated sulfuric acid. The operation of producing sulfuric acid in commercial process is very difficult and the costs of both equipment and operation are very expensive, because the complexity of the process, the corrosion of equipment at high temperature, and the presence of different impurities in the spent catalyst.
From the above description, there are some disadvantages using the traditionally commercialized process to treat the spent sulfuric acid: (1) To recover the regenerated sulfuric acid, several stages including in this process; combustion, purification, oxidation, purification again, and absorption have to be carried out on the spent sulfuric acid. The whole process is very complicated. (2) The corrosive compound is treated at very high temperature, so special material has to be chosen to construct the reactor, etc. (3) Based on the descriptions of (1) and (2), the costs of both equipment and operation are very expensive obviously. (4) Very large amounts of waste water, waste gas, and ashes are produced during the recovery process. Additional investment has to be funded to the facilities of retreatment for the waste materials. The additional investment is substantial. So, the traditionally commercialized process for the recovery of sulfuric acid from the spent catalyst of alkylation is very complicated and expensive.
Process for alkylation of alkanes and olefins in the presence of sulfuric acid as catalyst are well known and widely practiced on a commercial scale. Sulfuric acid reacts with hydrocarbons in such alkylation process to form organic impurities or by-products, dialkyl sulfates,acid alkyl sulfates and acid oils. The major portion of such by-products remains in the acid catalyst phase upon separation of an alkylation reaction zone effluent into a hydrocarbon effluent phase and a catalyst phase. In commercial alkylation processes, the hydrocarbon effluent is subjected to traditional distillation column for recovery of unreacted alkanes, olefins and alkylated hydrocarbon product. The unreacted alkanes or olefins are commonly recycled to the alkylation reactor for maintaining the ratio of isoparaffin to olefin above about 2.0. In a typical alkylation process, isoparaffins and olefins in the liquid phase are contacted with concentrated sulfuric acid of approximately 98% strength. The hydrocarbon and acid phases are separated and the acid is reused. The formation of by-products and the accumulation of water make the sulfuric acid be less strength. During repeated use in the processes, the acid becomes spent when the concentration of the acid falls to 85% to 90% concentration, it is necessary to withdraw the spent acid and supply fresh acid to the reaction zone. The spent acid is an approximately standardized material which varies but very little in composition between different alkylation plants. Although its composition is not precisely known, "spent alkylation sulfuric acid" is well-known in the industry by that name and those skilled in the art are well aware of its identity and characteristics as shown in Table 1. The data in Table 1 is a typical example.
Our previous U.S. Pat. No. 5,547,655 disclosed and claimed a method for the regeneration of spent alkylation sulfuric acid which comprises treating the acid in a vessel and removing organic impurities and water simultaneously through the active intermediates generated by heat, photolysis and electrolysis.
The present invention, the alkylation of alkanes and olefins can be carried out by using in situ regenerated spent sulfuric acid. The concentration of sulfuric acid in the alkylation zone can be kept at an almost constant level, such as 93%, 94% or any desired concentration between 90% to 98%, by the recycle regenerated sulfuric acid stream from the spent sulfuric acid regenerator. Based on the economic consideration the spent sulfuric acid concentration in the conventional process is about 90% or below 90% since the spent sulfuric acid is just a waste material and a sulfur resource of a sulfuric acid plant.
Economically, the best operating acid strength of the spent acid to discard is about 90% in a conventional alkylation process. However, both the quality and research octane number of gasoline from alkylation process are better by using a higher concentration sulfuric acid as catalyst raised by L. F. Albright and A. R. Goldsby, "Industrial and Laboratory Alkylations" in ACS symposium series 55, P.272, Washington, D.C., 1977. The combination of alkylation unit and regeneration unit makes this alkylation process be a higher efficiency and better gasoline quality integrated process. The acid regeneration can be done in refinery.
Based on the previous description and our previous invention, both the organic material and water can be removed simultaneously from the spent sulfuric acid in the presence or absence of other species, such as free radical, anion, cation, molecules and any other possible species.
The invention described above can be applied to a system containing sulfuric acid, organic material, water and nitric acid which is generated from a nitration process to produce mono-nitrotoluene (MNT), dinitrotoluene (DNT) and trinitrotoluene (TNT). In this process, concentrated H.sub.2 SO.sub.4 is a catalyst while nitric acid is one of the reactants. In general, a nitration process to produce TNT contains three stages. The organic compounds and water content in the spent nitrating mixture of H.sub.2 SO.sub.4 and HNO.sub.3 from the different stages are different. However, both the organic compounds as well as water can be removed simultaneously from any type of these three stages. Accordingly, an integrated process of nitration of spent acid can be developed obviously.
The chlor-alkali industry is an important process to produce chlorine gas as well as caustic soda. The chlorine gas from anolyte contains saturated humidity. Dried chlorine gas or liquid is the largest industrial product manufactured by electrolysis. The drying of wet chlorine gas is performed widely by passing the Net chlorine gas through the concentrated H.sub.2 SO.sub.4 to absorb the water. In general, the fresh sulfuric acid (98% by weight) was charged to the drying tower and the spent sulfuric acid is discarded at about 70% H.sub.2 SO.sub.4 and 30% H.sub.2 O. The efficiency of water absorption by a 70% H.sub.2 SO.sub.4 strength will be low. Furthermore, the spent sulfuric acid, in general, is discarded and treated by neutrulization or combustion process which is polluted and uneconomical. A continuous in situ integrated process for the regeneration of sulfuric acid from a drying tower of chlor-alkali process and recycling the regenerated sulfuric acid as an absorbant of water to the drying tower which comprises the steps of:
(a)withdrawing from a drying tower a liquid effluent comprising a sulfuric acid and water mixture, and a trace or very small amount of chlorine. PA1 (b)passing said liquid effluent into a regenerator maintained at a mild conditions having a temperature from -20.degree. C. to 250.degree. C. and pressure from one to 20 atms wherein said water reacts with active intermediates generated by electricity such that water decomposes and is removed. PA1 (c)recovering a totally or a substantially water free sulfuric acid from said regenerator and recycling the same to said drying tower. PA1 (1)withdrawing from an alkylation reactor an alkylation effluent comprising an olefinic hydrocarbon--sulfuric acid mixture, gas and liquid hydrocarbons. PA1 (2)introducing said alkylation effluent into a separator or settler wherein said effluent is separated into a gaseous hydrocarbon portion, liquid hydrocarbon portion, and sulfuric acid-olefinic hydrocarbon and water portion; PA1 (3)passing said sulfuric acid-olefinic hydrocarbon and water portion of said effluent to a regenerator maintained at a mild conditions having a temperature from -50.degree. to 250.degree. C. and pressure from one to 20 atms wherein both said organic impurities and water react with active intermediates generated by electricity such that both said organic impurities and water are removed simultaneously; PA1 (4)passing said hydrocarbon portions liquid and gaseous of step(2) to a fractionator; PA1 (5)recovering a totally or a substantially organic impurities and water free sulfuric acid from said regenerator and recycling the same to said alkylation unit.